Researchers studied a series of brain scans of children from preschool through early adolescence and found two times the growth in the hippocampus—the part of the brain associated with learning, memory and regulating emotions—in kids whose mothers supported and nurtured them during the preschool years.

Whoa! And get this: The hippocampus appeared smaller in kids with less supportive moms, even if they eventually became more supportive during the elementary or middle school years.

"This study suggests there's a sensitive period when the brain responds more to maternal support," said lead author and child psychiatrist Joan L. Luby, M.D., a professor at Washington University School of Medicine in St. Louis. "The parent-child relationship during the preschool period is vital, even more important than when the child gets older."

Wondering how the researchers went about quantifying the moms' ability to nurture? (I know I was!) Luby said the moms were given a score after being observed with their children in moderately stressful conditions—like being asked to complete a task while their child is handed an attractive gift but told not to open it right away.

"It's a stressful condition like those that happen multiple times each day in any given family, like when you're cooking dinner and a child wants attention," Luby explained. "The child needs something, but you have something else to do, so it challenges your parenting skills."

Fair enough. Moms who kept their cool and completed the assigned tasks while offering emotional support to their kids got high marks for being nurturing and supportive, while the ones who dismissed their kids or who acted out scored lower. Then the researchers studied the brain scans and found the hippocampus correlation.

The big takeaway here, obviously, is to openly support and nurture your kids from a very young age. But Luby says we should also be focused on helping parents learn different ways to accomplish this. "Early maternal support affects the child's brain development. We also know that providing support to parents can have a positive impact on other behavioral and adaptive outcomes in children," she said. "So we have a very logical reason to encourage policies that help parents become more supportive."